Sortilin is a receptor that has been reported to mediate pro-apoptotic effects of pro-neurotrophins and to mediate trafficking and sorting of neurotrophin receptors (Nykjaer et al, 2012, Trends Neurosci. 2012; 35(4):261-70; Glerup et al, Handb Exp Pharmacol, 2014; 220:165-89, Carlo et al, J Mol Med (Berl). 2014 September; 92(9):905-11). A number of sortilin ligands have been identified including neurotensin for which a high affinity binding site was localized by x-ray crystallography to inside a beta propeller tunnel in the sortilin molecule (Quistgaard et al, Nat Struct Mol Biol. 2009 January; 16(1):96-8; Quistgaard et al, Protein Sci. 2014, September; 23(9):1291-300). More recently, sortilin was shown to function as a high affinity receptor for the growth factor progranulin (PGRN, Hu et al. Neuron. 2010 Nov. 18; 68(4):654-67.
PGRN ((proepithelin, granulin-epithelin precursor, PC-cell-derived growth factor, acrogranin)) is a secreted glycosylated protein with anti-inflammatory and neurotrophic-like actions (For a recent review, see Nguyen, Trends Endocrinol Metab. 2013 December; 24(12):597-606). PGRN is proteolytically cleaved to granulins, but much remains to be learned regarding the physiological role of PGRN and granulins and the identity of their receptors. PGRN has been implicated in several cellular functions including cell cycle regulation and cell motility (He, Z. & Bateman, A., J. Mol. Med. 57:600-612 (2003); Monami, G., et al., Cancer Res. (5(5:7103-7110 (2006)), wound repair, inflammation (Zhu, J., et al., Cell 777:867-878 (2002)), induction of growth factors such as vascular endothelial growth factor (VEGF) (Tangkeangsirrsin, W. & Serrero, G, Carcinogenesis 25.1587-1592 (2004)), and tumorigenesis (He, Z. & Bateman, A., J. Mol. Med. 81:600-612 (2003), Monami, G., et al., Cancer Res (5(5:7103-7110 (2006); Serrero, G., Biochem Biophys. Res. Commun. 505-409-413 (2003), Lu, R & Serrero, G., Proc. Natl Acad Sci U.S.A. 98 142-147 (2001); Liau, L M., et al., Cancer Res. 60:1353-1360 (2000)). PGRN has been reported to bind the TNF receptor (Tang W et al., Science 2011, 332(6028):478-84). but this observation has been challenged by others (Chen et al., J Neurosci. 2013, 33(21):9202-9213).
The binding of PGRN to sortilin has been mapped to the neurotensin site and reported to be mediated solely through the PGRN C-terminal domain (Zheng et al. PLoS One. 2011; 6(6):e21023; Lee et al. Hum Mol Genet. 2013) in a manner similar to neurotensin and in accordance, neurotensin has been shown to block the interaction of sortilin with PGRN and other ligands. Upon binding, sortilin mediates lysosomal clearance of PGRN and thereby regulates extracellular PGRN levels (Hu et al. 2010). Thus, knockdown or overexpression of sortilin have been shown to regulate extracellular PGRN levels in cell culture (Carrasquillo et al. Am J Hum Genet. 2010 Dec. 10; 87(6):890-7) and in mice, sortilin deficiency was reported to increase PGRN levels and to restore plasma and brain PGRN-levels in PGRN+/−mice (Hu et al. 2010). Interestingly, a single nucleotide polymorphism (SNP) near sortilin was associated with decreased plasma PGRN and increased sortilin mRNA levels (Carrasquillo et al. Am J Hum Genet. 2010 Dec. 10; 87(6):890-7). These observations suggest that sortilin is a key regulator of extracellular PGRN.
PGRN has been linked to frontotemporal dementia (FTD), a progressive dementia characterized by behavioral and semantic changes, as well as frontotemporal lobar degeneration (FTLD) and neuronal inclusions containing TAR DNA Binding Protein-43 (TDP-43) or tau inclusions (Baker et al, 2006, Nature. 2006 Aug. 24; 442(7105):916-9; Cruts et al, Nature 442: 920-924 (2006); Am J Hum Genet. 2010 Dec. 10; 87(6):890-7, M et al, Trends in Genetics 24: 186-194 (2008)). The majority of sporadic and familial FTD cases show TDP-43 pathology (˜50%) similar to ALS and FTD-TDP43 and ALS are by some considered to constitute a disease spectrum (Ito D Neurology. 2011 Oct. 25; 77(17):1636-43; Boxer A L et al, Alzheimers Dement. 2013 March; 9(2):176-88; Rademakers et al, Nat Rev Neurol. 2012 August; 8(8): 423-434) due to common pathologies and genetic factors and some overlap in symptomatology. No disease-modifying treatment options are available for FTD. A subset of frontotemporal dementia patients with TDP-43 pathology have loss of function mutations in the granulin gene (GRN) resulting in PGRN haplo-insufficiency. To date, 69 different mutations in the granulin gene, all resulting in reduced PGRN levels and/or function, have been associated with FTD and it is believed that raising extracellular PGRN in plasma and brain would counteract the disease process.
PGRN mutations have also been linked with Alzheimer's disease (AD) (Sheng et al., 2014, Gene. 2014 Jun. 1; 542(2):141-5; Brouwers et al., 2008, Neurology. 2008 Aug. 26; 71(9):656-64) suggesting that PGRN deficiency may play an important role in AD pathogenesis. Furthermore, neuroprotective effects of PGRN in mouse AD models have been observed (Minami et al, 2014, Nat Med. 2014 October; 20(10):1157-64) providing support for the view that enhanced PGRN may be beneficial in AD and possibly other neurodegenerative conditions.
The present application describes the generation and identification of anti-human Sortilin antibodies which can regulate PGRN in cellular models and in mice. Those antibodies surprisingly bind to a region on Sortilin which is distant to the previously reported progranulin binding site, the so-called neurotensin-site, and yet are capable of inhibiting Sortilin-PGRN interaction and of thereby increasing extracellular PGRN.
The inventors have defined six Sortilin binding regions and surprisingly identified that the most efficacious antibodies bind a region (“region D”). As PGRN has neuroprotective and anti-inflammatory effects, the inventors' findings indicate that such antibodies targeting Sortilin are likely to have a beneficial effect in the treatment of a range of neurodegenerative disorders including FTD/FTLD. A subgroup of these patients carry a mutation in the gene encoding PGRN leading to haploinsufficiency. Sortilin antibodies are therefore likely to have similar therapeutic benefits for patients suffering from other TDP-43 proteinopathies and diseases in which PGRN levels may influence TDP43-function and pathology, including ALS and AD.